1. Field of the Invention
The present invention relates to a program, a controller, and a boiler system that are configured to control a boiler group including boilers each of which has a plurality of stepwise combustion positions.
2. Description of the Related Art
Conventionally, in the case of controlling the combustion in a boiler group including a plurality of boilers, technologies have been disclosed that are related to the control of the boiler group in which a combustion quantity is calculated based on a steam pressure to determine the number of the boilers subject to combustion based on results of the calculations.
In those boiler systems, the number of the combustion subject boilers (combustion positions) is set corresponding to the header pressure so that combustion may occur at a predetermined number of the combustion positions in accordance with the priority sequence numbers according to the present time header pressure.
In such a control method, as shown in, for example, FIG. 9A, in the case of operating four combustion shiftable boilers (Nos. 1 to 4) and one preliminary can (No. 5) in a boiler group including five three-position boilers (Nos. 1 to 5, having a differential evaporation quantity of 500 (kg/h)) at each combustion position at a set pressure of 1.0 (MPa) and an allowable pressure width of 0.2 (MPa), each combustion position is allotted 0.025 (MPa). Therefore, if the present time pressure is 0.87 (MPa), the six combustion positions are subject to combustion. It is to be noted that in FIGS. 9A, 9B, and 9C, a hatched frame denotes the combustion position which is provided with a combustion output.
However, in a case where the number of preliminary cans (Nos. 4 and 5) is increased to two owing to, for example, a failure, if a pressure deviation is equal to or less than 0.15 (MPa), although the combustion quantity can be controlled stepwise all over the allowable pressure width, the present time pressure lowers to 0.825 (4 Pa) so that the pressure deviation may go beyond 0.15 (MPa) up to 0.175 (MPa), whereupon combustion needs to occur at seven combustion positions, so that one combustion position lacks because combustion can occur only in the three boilers as against seven combustion positions where combustion needs to occur as shown in FIG. 9B, thereby making it difficult to conduct control appropriately. (A shaded portion in FIG. 9B denotes a lacking position.)
On the other hand, in a case where the preliminary can (No. 5 boiler) has shifted to a combustion shiftable boiler to increase the number of combustion shiftable boilers to five, if the present time pressure variations are within the range of the allowable pressure width of 0.20 (MPa), for example, the pressure deviation of 0.15 (MPa), combustion is output only to six combustion positions as shown in FIG. 9C, so that the No. 5 boiler is put into essentially the same state as the preliminary can unless the present time pressure variations fall outside the allowable pressure width of 0.20 (MPa).
Accordingly, loads are concentrated to the No. 1 through No. 4 boilers, to make it difficult to carry out effective operations by means of distribution of the loads.
To solve the problem, there are technological demands for operating a boiler group effectively even if the number of the combustion shiftable (operational) boilers varies.